Sponge



FIG. 1 is a perspective view showing the new design for a sponge;

FIG. 2 is a top view thereof, the bottom view being a mirror image thereof;

FIG. 3 is a right side view thereof, the left side view being a mirror image thereof; and,

FIG. 4 is a front view thereof, the rear view being a mirror image thereof. 

The ornamental design for a sponge, as shown and described. 